1. Field of the Invention
The present invention relates to a video cable between a computer and monitor, more particularly, to a digital video signal interface module that is able to lengthen a transferring distance of a computer outputting a digital video output and a monitor inputting a digital video input.
2. Description of Related Art
The video signal outputted from a conventional computer is an analog type or a digital type. The analog type is generally applied to a conventional cathode ray tube (CRT) type and the digital type is generally applied to the monitors such as a liquid crystal display (LCD). Accordingly, A-D converter is used when the LCD monitor is used for the computer outputting the analog video output.
However, many computers that output the digital video signals have been emerged according to a popularization of the LCD monitors. Subsequently, many people can enjoy images of the clean digital signals without an additional A-D converter.
But, there is a problem that the digital signals cannot be transferred because a frequency of a digital interface type is a high frequency of hundreds MHz to several GHz.
Accordingly, an additional amplifier has been used for the monitor installed in ships, trains, medical instruments, outdoor billboards, departments, and elevators, etc., when a distance between the computer and the monitor is about 5 to tens meters.
FIG. 1 shows a configuration drawing illustrating a system for transferring the digital signals to a long distance adopted for a Digital Visual Interface (DVI) standard of a conventional computer.
As shown in FIG. 1, the conventional system is configured as a computer (1) which is able to output the digital video signals, an amplifier (4), a receiver (5), and a LCD monitor (2). One terminal of a first digital exclusive use line (7) is connected to a video output terminal (not shown) of the computer (1) and another terminal of the first digital exclusive use line (7) is connected to the amplifier (4). The amplifier (4) generates signals of Red (R), Green (G), Blue (B), Clock (C) after amplifying the digital signals using an external power supply (6). The receiver (5) transfers the R, G, B, C signals to the LCD monitor (2) through a second digital exclusive use line (10) after adjusting the R, G, B, C signals to regular voltage levels using the external power supply (6). The rapid R, G, B, C signals are transferred through a Bayonet Neil-Concelman (BNC) connector line (8).
Also, a Data Display Channel (DDC) signal for transferring an information of the monitor (2) to the computer (1) is consisted of a DDC clock, a DDC data and a Hot Plug Detect (HPD). The DDC signal is connected between the amplifier (4) and the receiver (5) through an additional DDC line (9) greatly attenuating the signals. If necessary, a digital projector (3) can be used in lieu of or together with the monitor (2). Because the above cited system is used, the distance between the amplifier (4) and the receiver (5) becomes long several to tens meters.
However, there are problems that the amplifier (4) and the receiver (5) of the conventional system require the external power supply (6), two digital exclusive use lines (7, 10), four BNC lines (8), and a complex DDC line (9), the system is complexed, and a production cost is high because the components are many, and an installation is inconvenient, etc.
FIG. 2 is a configuration drawing that signals for all digital interfaces are consisted of light before a system of the present invention is realized. As shown in FIG. 2, the system is roughly consisted of a computer (1), a transmitter (21), an optic fiber (27), a receiver (23), and a LCD monitor (2), R, G, B, C signals, a DDC date, a DDC clock (six channels) outputted from the computer (1) is respectively converted to optic signals in six laser diodes (28) by a laser driver (20). The converted optic signals are transferred to a long distance through the six optic fibers (27). Six photodiodes (29) restore the received optic signals to electric signals and a Photo-Diode (PD) amplifier (22) amplifies a weak electric signal to a predetermined voltage level. The amplified signal is transferred to and displayed on the LCD monitor (2).
On the other hand, the system has an additional two channel laser driver (26) and the laser diode (28) in the receiver (23), and an additional two channel PD amplifier (24) in the receiver (21). And, additional two lines of the optic fibers are used for transferring the signals.
When all signals are converted into the optic signals, eight lines of the optic fibers are required, and this results in combining six channels system with two channels system. The production cost becomes raised and a transferring velocity of the DDC signal is too late to transfer the optic signal because of a low frequency of 100 kHz.
Also, A Digital Visual Interface (DVI) standard of the digital interface must essentially has a HPD function in an operating system beyond window 95. The HPD function is operated by detecting a DC +5 V, but the above cited system cannot support the HPD function. That is, for supporting the HPD function in the above cited system, an additional signal is inserted into other signals and transferred, and the receiver must detect the additional signal using a micom. However, the method becomes more complicated in a structure of the system and the production cost becomes raised.
The extra problem is that the power supply must be supplied from the outsides in order to operate functional devices of the receiver because the extra pins do not exist in order to supply the power supply from the monitor in the receiver under DVI, DFP, or Low Voltage Differential Signalling (LVDS) of the digital interface standards.